Latch needles are mounted in a circular knitting machine in such a way that their backs are in contact with the needle bed in the needle grooves in the cylinder. As the cylinder rotates, the latch needles rotate at a high speed, while at the same time fixed cams established opposingly to the needle bed act on the butts of the latch needles, reciprocating the latch needles at a high speed. As the knitting speed increases, the force with which each cam acts on these needle butts also increases and is transmitted to the needle head as a shock wave, causing broken needle heads.
In an attempt to solve this problem, it has been proposed to incorporate into the needles means to absorb the shock wave that is generated and transmitted to the needle head when the cam acts on the butt. This proposal includes providing the needle trunk, which is between the butt and the needle head, with cutouts on the upper and lower sides. It has also been postulated that the thinner the needle shaft and the bridge that are left after the cutouts have been made the more effective the shock absorbing performance. This is a so-called meander-type latch needle, which is widely used today. Various and sundry other attempts at latch needles with shock absorbing capabilities have also been proposed.
In these so-called meander-type latch needles, depending on the structure of the knitting machine (for example a double knit machine employing a dial needle or a needle that is controlled by a special needle-selecting structure), there is a limit to how far the butt and the needle head can be distanced from each other, making it impossible to provide the needle trunk between the butt and the needle head with a shape that effectively absorbs the shock wave.
Another type of latch needle has been proposed based on the concept of completely blocking the shock wave, which is generated when the cam hits the butt, before it reaches the needle head. According to this concept, the shock wave is blocked by splitting the head part and the butt part, which were conventionally one unit. For example, Japanese Utility Model Application No. A-55-180788, Japanese Utility Model Application No. A-56-78896, and U.S. Pat. Nos. 2,431,635 and 3,411,327 propose this type of latch needle in one form or another. According to these utility models and patents, the working needle and the butt needle engage at the position of the butt of the butt needle or at a position closer to the front of the butt needle.
As for the latter type, i.e., the split-type latch needle, the variations disclosed in the patents and utility models mentioned above are rarely used in practice now. The reason is believed to be that none of them have produced satisfactory results.